Anti-torque rotor for a helicopter

ABSTRACT

An anti-torque rotor is described comprising: a mast rotatable about a first axis; a plurality of blades rotatable about respective second axes; an element slidable along the first axis with respect to the mast, rotating integrally with the mast and operatively connected to the blades; a control rod slidable along axis; a first bearing with a first ring rotating integrally with element, a second ring radially internal to the first ring with respect to the first axis and a plurality of first rolling bodies; a third ring sliding integrally with the control rod along the first axis and angularly fixed with respect to the first axis; and a locking element arranged in a standard configuration, in which it prevents the relative rotation of the second and third rings and movable from the standard configuration to at least one emergency configuration, in which it renders the second ring free to rotate with respect to the third ring, when the first bearing is in a failure condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from European patent applicationno. 19182720.3 filed on Jun. 26, 2019, the entire disclosure of which isincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an anti-torque rotor for a helicopter.

BACKGROUND ART

Helicopters are known to basically comprise a fuselage, a main rotorpositioned on the top of the fuselage and rotatable about an axisthereof, and an anti-torque rotor arranged at the tail end of thefuselage.

Helicopters also comprise, in a known manner, one or more power units,such as turbines for example, and a transmission unit interposed betweenthe turbines and the main rotor and adapted to transmit motive powerfrom the turbines to the main rotor itself.

In greater detail, the anti-torque rotor, in turn, basically comprises:

-   -   a mast rotatable about a first axis;    -   a hub rotatable about the first axis; and    -   a plurality of blades hinged on said hub, projecting in a        cantilever fashion from the hub and each extending along        respective second axes transversal to the first axis.

The mast of the anti-torque rotor is driven in rotation by a set ofgears driven by the main transmission unit.

The blades of the anti-torque rotor rotate integrally with the mastabout the first axis and can be selectively tilted about the secondaxis, so as to be able to vary the respective angles of attack andconsequently adjust the thrust exerted by the anti-torque rotor.

In order to adjust the angles of attack of the respective blades,anti-torque rotors comprise:

-   -   a rod, operatively connected to a pedal operable by the pilot        through a mechanical connection or fly-by-wire link and sliding        inside the mast along the first axis, but angularly fixed with        respect to the first axis;    -   a control element, also known as a “spider”, integrally        rotatable with the mast about the first axis and equipped with a        plurality of arms connected to respective blades in an eccentric        position with respect to the associated second axes; and    -   a rolling bearing, mounted in a sliding manner with respect to        first axis, interposed between the rod and the control element,        and configured so as to transmit an axial load from the rod to        the rotatable element.

More specifically, the rolling bearing, in turn, comprises:

-   -   a radially outer ring fastened on the control element;    -   a radially inner ring fastened to the control rod; and    -   a plurality of rolling bodies, which roll in respective tracks        defined by the radially inner and outer rings.

In a normal operating condition of the bearing, the rolling bodies allowrotation of the outer ring with respect to the inner ring and theconsequent rotation of the control element with respect to the rod.

Operation of the pedal causes the control rod to slide parallel to thefirst axis. This sliding causes, via the rolling bearing, the controlelement to slide parallel to the first axis along a given path oftravel.

This sliding causes rotation of the blades about the associated secondaxes, so as to vary the respective angles of attack by equal amountsassociated with the given path of travel.

From the foregoing, it follows that a possible failure of the rollingbearing would risk making the anti-torque rotor substantiallyuncontrollable, causing a hazardous situation for the helicopter.

In particular, a failure situation might occur in the case where rollingbodies and/or the tracks of the inner or outer ring become damaged, forexample due to the accidental introduction of foreign bodies inside thebearing, the loss of lubricating grease, damage to the tracks orsurfaces of the rolling bodies.

In this condition, instead of allowing the relative rotation of thecontrol element to the control rod, the rolling bearing would improperlytransfer a twisting moment, progressively growing over time, from theouter ring to the inner ring.

This twisting moment would be transmitted to the control rod, generatinga risk of damaging the control rod.

The failure condition of the rolling bearing is normally preceded by anincrease in the torque acting on the inner ring and an increase intemperature and vibrations in the area around the rolling bearing.

There is awareness in the industry of the need to reduce the risk ofthese failure conditions making regulation of the blades' angle ofattack ineffective, thereby making the thrust of the anti-torque rotorand the yaw angle of the helicopter substantially uncontrollable.

There is also awareness in the industry of the need to ensure correctcontrol of the anti-torque rotor, even in the event of failure of therolling bearing.

Finally, there is awareness in the industry of the need to promptlyidentify the incipient failure state of the rolling bearing and toprovide a clear and immediate indication to the crew.

U.S. Pat. No. 9,359,073 describes an anti-torque rotor for a helicopteraccording to the preamble of claims 1, 16, 28, 35, 46, 57 and 69.

In greater detail, U.S. Pat. No. 9,359,073 describes an anti-torquerotor comprising a mast, a rod, and a first and second bearing arrangedin series.

The first bearing comprises a first ring rotatable with the mast and asecond ring.

The second bearing comprises a third ring and a fourth ring.

The third ring of the second bearing and the first ring of the firstbearing are connected to each other in a non-rotatable manner.

In particular, the first and the second ring respectively define a firstand a second track for first rolling bodies of the first bearing.

The third and the fourth ring respectively define a third and a fourthtrack for the second rolling bodies.

In other words, each first, second, third and fourth ring define arespective first, second, third and fourth track. The anti-torque rotoralso comprises a locking device interposed between the third and thefourth rings and adapted to prevent rotation of the third ring withrespect to fourth ring. This locking device comprises an element that isbreakable in the case of the first bearing failure and not breakable inthe case of correct operation of the first bearing.

The solution shown in U.S. Pat. No. 9,359,073 is particularly complex asit requires using two rolling bearings and a locking device.

In particular, the solution shown in U.S. Pat. No. 9,539,073 requiresfour rings for defining four tracks and the first and the second bearingare axially spaced with respect to one another.

This renders the solution shown in U.S. Pat. No. 9,539,073 particularlycumbersome and unsuitable to be easily fitted in the reduced axial sizeof the tail rotor of the helicopter.

Furthermore, both the first and the second bearing comprise a singlering of spherical rolling bodies.

Having the single ring of rolling bodies a small rotation stiffness, thebreakable element of the locking device can only transmit axial loadsparallel to the rotation axis of the mast.

Accordingly, the solution shown in U.S. Pat. No. 9,539,073 is effectivesubstantially in transmitting loads parallel to the rotation axis of themast only.

Furthermore, the use of a single ring of spherical rolling bodiesinevitably causes the presence of axial loads, which can result inannoying vibrations and noise.

Furthermore, due to the presence of a single ring of spherical rollingbodies, the bearings of renders are particularly exposed to the falsebrinelling wear damage mechanism, i.e. to the occurrence of hollow spotsthat resemble brinell dents and are due to wear caused by vibration andswaying at the contact points between the rolling bodies and the tracks.

DISCLOSURE OF INVENTION

The object of the present invention is to provide an anti-torque rotorthat enables satisfying at least one of the aforementioned needs in asimple and inexpensive manner.

The aforesaid object is achieved by the present invention, in so far asit relates to an anti-torque rotor as defined in claims 1, 16, 28, 35,46, 57 and 69.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, three preferredembodiments are described hereinafter, purely by way of non-limitativeexample and with reference to the accompanying drawings, in which:

FIG. 1 is a top view of a helicopter comprising an anti-torque rotoraccording to a first embodiment of the present invention;

FIG. 2 is a section along line II-II of FIG. 1, on a highly enlargedscale and with some parts not shown for the sake of clarity;

FIG. 3 is a perspective view, on a highly enlarged scale, of somecomponents of the anti-torque rotor of FIGS. 1 and 2;

FIG. 4 is a side view of the components of FIG. 3 in a standardconfiguration;

FIG. 5 is a section along line V-V of FIG. 4 in the standardconfiguration;

FIG. 6 is a side view of the component of FIGS. 3 and 5 in a firstemergency configuration;

FIG. 7 is a section along line VII-VII of FIG. 6 in the first emergencyconfiguration;

FIG. 8 is a side view of the component of FIGS. 3 to 7 in a secondemergency configuration;

FIG. 9 is a section along line IX-IX of FIG. 8 in the second emergencyconfiguration;

FIG. 10 is the section of FIG. 5, with hatched parts for the sake ofclarity;

FIG. 11 is a section along line XI-XI of FIG. 3;

FIG. 12 is a perspective view, on a highly enlarged scale, of somecomponents of the anti-torque rotor according to a second embodiment ofthe invention in the standard configuration;

FIG. 13 is a section along line XII-XII of FIG. 12;

FIG. 14 is a perspective view, on a highly enlarged scale, of somecomponents of the anti-torque rotor according to a third embodiment ofthe present invention in the standard configuration;

FIG. 15 is a perspective view of the third embodiment of the anti-torquerotor in one of the first and second emergency configuration; and

FIGS. 16 and 17 are section taken along lines XV-XV and XVI-XVIrespectively of FIGS. 14 and 15.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, reference numeral 1 indicates a helicopterbasically comprising:

-   -   a fuselage 2;    -   one or more turbines 5;    -   a main rotor 3 positioned on the top of the fuselage 2 and        rotatable about an axis A; and    -   an anti-torque rotor 4 located at a tail end of the fuselage 2        and rotatable about an axis thereof, transversal to axis A.

The helicopter 1 also comprises a transmission unit, in itself known andnot shown, which transmits motive power from the turbines 5 to the mainrotor 3.

In turn, the transmission unit comprises:

-   -   a gear train, which transmits motive power from the turbine 5 to        the main rotor 3; and    -   a shaft 13, which transmits motive power from the gear train 12        to the anti-torque rotor 4.

In a known manner, the main rotor 3 is adapted to provide orientablethrust that enables lift-off and forward flight of the helicopter 1.

The anti-torque rotor 4 generates a thrust, which causes a countertorque on the fuselage 2.

This counter torque is directed in the opposite direction to the torqueexerted by the main rotor 3.

According to the amount of thrust generated by the anti-torque rotor 4,it is therefore possible to orientate the helicopter 1 according to adesired yaw angle, or vary said yaw angle depending on the manoeuvrethat it is wished to perform.

Referring to FIGS. 2 to 11, the anti-torque rotor 4 basically comprises:

-   -   a mast 6 rotatable about an axis A and operatively connected to        the shaft 13 in a known manner;    -   a plurality of blades 8, three in number in the case shown,        which extend in a cantilever fashion along respective axes B        transversal to the axis A; and    -   a hub 9 externally fastened to a portion of the mast 6,        integrally rotatable with the mast 6 about axis A and on which        the blades 8 are hinged.

More specifically, the blades 8 are hinged on the hub 9 so as to be:

-   -   integrally rotatable with the hub 9 and the mast 6 about axis A;        and    -   tiltable about their respective axes B by the same angles and        simultaneously over time, so as to vary the respective angles of        attack.

In particular, the hub 9 comprises a plurality of connection elements 18projecting radially with respect to axis A for connection to therespective blades 8. Each blade 8 also comprises a root portion 14arranged radially inward with respect to the axis A and hinged on theassociated connection element 18 of the hub 9.

In order to vary the aforementioned angles of attack, the anti-torquerotor 4 also comprises:

-   -   a flight control 15 (only schematically shown in FIG. 1)        operable by the pilot, for example a pedal;    -   a control rod 10 sliding parallel to the axis A and operable by        the flight control 15, by means of a mechanical connection or a        fly-by-wire method;    -   a control element 16 rotatable integrally with the mast 6 about        axis A and connected to the blades 8 in an eccentric manner with        respect to the associated axes B; and    -   a bearing 17 interposed between the control rod 10 and element        16 and sliding, jointly with the control rod 10, parallel to        axis A.

More specifically, the mast 6 is hollow.

The mast 6 also comprises (FIG. 2):

-   -   an axial end 20;    -   a further axial end, not shown, open and opposite to end 20; and    -   a main portion 22 interposed between the axial end 20 and the        further axial end, on which the hub 9 is fitted, and adapted to        receive motive power from the shaft 13 (FIG. 1) via a flange 19.

The control rod 10 is partly housed inside the mast 6.

The control rod 10 also comprises:

-   -   a first axial end (not shown) and connected to the shaft 13;    -   a second axial end 24 (FIG. 2) connected to the bearing 17 and        opposite to the first axial end; and    -   a main body 25 passing through the end 20 and the further axial        end of the mast 6.

The main body 25 further comprises, starting from end 24 and proceedingalong the axis A:

-   -   a segment 26 of larger diameter than end 24;    -   a segment 27 of larger diameter than segment 26; and    -   a shoulder 28 radially interposed between segments 26 and 27.

End 24 is arranged externally to the mast 6.

The first end is operatively connected to the flight control 15 by alinkage (not shown) or by a fly-by-wire type of activation.

Element 16, in turn, comprises (FIG. 2):

-   -   a tubular body 40, partly housed in the mast 6 and connected to        the mast 6 in a sliding manner with respect to axis A, and        partly housing the control rod 10;    -   a flange 42 extending orthogonally to axis A and fastened to the        tubular body 40 on the end opposite to the mast 6; and    -   a plurality of levers 43 hinged on the flange 42 about        respective axes C transversal to axis A and hinged on respective        blades 8 in eccentric positions with respect to the associated        axes B.

The flange 42 and the bearing 17 are housed outside the mast 6 andsurround the control rod 10.

The flange 42 is connected to the mast 6 by a single variable-lengthbellows coupling 44, which enables sliding along the axis A.

The levers 43 are generally inclined with respect to axis A and extendfrom the flange 42 towards the end 20.

The translation of the control rod 10 along axis A causes, via thebearing 17, the translation of element 16.

Following the sliding of element 16 along axis A, the levers 43 changetheir inclination with respect to axis A by the same mutually identicalangles, causing the simultaneous rotation of the blades 8 about theirrespective axes B by the same mutually equal angles.

In particular, the levers 43 are hinged on the root portions 14 of therespective blades 8.

The bearing 17 is able to transmit axial loads parallel to axis A inboth directions.

In other words, the bearing 17 is configured so that translation of thecontrol rod 10 along axis A in both directions causes the translation ofelement 16 in the same directions.

In this way, the bearing 17 connects the control rod 10 and element 16in an axially integral and angularly movable manner with respect to axisA.

The bearing 17, in turn, comprises:

-   -   a radially outer ring 30 integrally rotatable with element 16;    -   a radially inner ring 31 integrally sliding with the control rod        10; and    -   a plurality of rolling bodies 32, a double ring of balls in the        case shown, rolling on respective tracks 33 and 34 defined by        the respective rings 30 and 31.

In the case shown, the ring 30 has a pair of shoulders 35 and 36 atmutually opposite sides, projecting radially towards ring and definingrespective axial abutment surfaces for the rolling bodies 32. Theshoulders 35 and 36 define track 33.

The rolling bodies 32 are, in particular, axially interposed between theshoulders 35 and 36.

Furthermore, ring 30 is made in two half-rings 41, arranged axially incontact with each other in the case shown.

Ring 30 is force-fitted, in a radially outer position, on the tubularbody 40 of element 16.

Ring 31 comprises a shoulder 37 axially interposed between shoulders 35and 36, projecting radially towards ring 30. These shoulder 37 isaxially interposed between the rolling bodies 32 on a plane of symmetryof the bearing 17 radial to axis A.

Furthermore, the ring 30 is fastened on the tubular body 40 of element16 on the opposite side to flange 42 in a direction radial to axis A.

The bearing 17 also comprises two annular cages 39 adapted to keep therolling bodies 32 of the respective rings angularly and equispaced fromeach other.

Ring 31 is radially inner with respect to ring 30 relative to axis A.

In particular, track 34 is radially inner with respect to track 33relative to axis A.

Hereinafter in this description, the term “failure” of the bearing 17means any effective or incipient emergency condition in which thebearing 17 is no longer able to transmit only an axial load from thecontrol rod 10 to element 16, i.e. causing axial translation of element16 in both directions, following the axial translation of the controlrod 10, without generating any twisting moment on the control rod 10.

By way of non-limitative example, a first (incipient) emergencycondition arises when the rolling bodies 32 and/or the tracks 33 and 34become damaged, for example, due to foreign bodies accidentally enteringthe bearing 17 or the loss of lubricating grease.

In this first emergency condition, ring 31 of the bearing 17 issubjected to a twisting moment.

Furthermore, the first emergency condition of the bearing 17 isgenerally associated with an increase in temperature and/or vibrationlevel of the area around the bearing 17 and/or of the torque transmittedto the ring 31.

A second emergency condition arises when the rolling bodies 32 of thebearing 17 break, such that the control rod 10 becomes axially movablewith respect to element 16.

The anti-torque rotor 4 also advantageously comprises:

-   -   a further ring 50 sliding integrally with said control rod 10        along axis A and angularly fixed with respect to axis A;    -   a plurality of rolling bodies 51, which are interposed between        said rings 31 and 50 and roll on respective tracks 52 and 53 of        the respective rings 31 and 50; and    -   a locking element 55 arranged in a standard configuration, in        which it prevents the relative rotation of the rings 31 and 50,        when the bearing 17 is in a normal operating condition; the        locking element 55 is movable from the standard configuration to        at least a first or second emergency configuration, in which it        renders ring 50 free to rotate with respect to ring 31 about        axis A, when the bearing 17 is in the failure condition.

In particular, rings 30, 31, 50 are coaxial and extend about axis A.

Still more precisely, ring 50 is radially inner with respect to ring 31relative to axis A.

Furthermore, track 53 is radially inner with respect to track 52relative to axis A.

In particular, ring 31 is formed in a one-piece and integrally definestracks 34, 52.

In greater detail, when the bearing 17 is in a normal operatingcondition and the locking element 55 is in the standard configuration,ring 30 rotates about axis A and rings 31 and 50 are angularly fixedwith respect to axis A.

In this situation, ring 50 is substantially inactive.

Contrariwise, when the bearing 17 is in a failure condition and thelocking element 55 is in the first or second emergency configurations,rings 30 and 31 rotate about axis A and ring 50 is angularly fixed withrespect to axis A. In this condition, the set of rings 30 and 31 andring 50 form a backup bearing 54 (FIGS. 5, 7, 9 and 10), which enablescontrol of the anti-torque rotor 4 even in failure conditions of thebearing 17.

In greater detail, the locking element 55 automatically moves from thestandard configuration to the first emergency configuration when, in theevent of failure of the bearing 17, the temperature of the bearing 17exceeds a respective threshold value.

The locking element 55 automatically moves from the standardconfiguration to the second emergency configuration when, in the eventof failure of the bearing 17, the vibrations in the area of the bearing17 exceed a respective threshold value and/or the torque transmittedfrom ring 30 to ring 31 exceeds a respective threshold value.

The backup bearing 54 is able to transmit axial loads parallel to axis Ain both directions. In other words, the backup bearing 54 is configuredso that the translation of the control rod 10 along axis A in bothdirections continues to cause the translation of element 16 in the samedirections, even in the event of failure of the bearing 17.

Ring 50 also comprises:

-   -   a radially outer surface 57, which comprises two shoulders        axially opposing each other, inclined with respect to axis A and        defining respective tracks 52 and 53; and    -   a radially inner surface 58, opposite to surface 57 and        force-fitted on segment 26 of the control rod 10.

The rolling bodies 51 are, in the case shown, conical rollers withrespective lateral surfaces convergent towards axis A. In particular,the conical rollers are arranged in an X, i.e. with the respective axesconverging on axis A.

The backup bearing 54 further comprises two annular cages 59 adapted tokeep the rolling bodies 51 of the respective rings angularly and evenlyspaced out from each other.

Furthermore, in the case shown, ring 50 is made in two half-rings 45arranged in contact with one another axially.

The locking element 55 is angularly fixed with respect to axis A, bothin the standard configuration and in the first or second emergencyconfigurations.

When arranged in the standard configuration, the locking element 55 isaxially integral with rings 31 and 50 and with the control rod 10.

When arranged in the first or second emergency configuration, thelocking element 55 can instead slide parallel to axis A with respect torings 31 and 50 and the control rod 10.

More specifically, the locking element 55 is arranged with respect torings 31 and 50 and with reference to axis A:

-   -   in an inserted position (FIGS. 4 and 5), reached when the        locking element 55 is in the standard configuration; and    -   in an extracted position (FIGS. 6 to 9), reached when the        locking element 55 is arranged in the first or second emergency        configuration.

A first axial distance between the locking element 55 set in theinserted position and the rings 31 and 50 is less than a second axialdistance between the locking element 55 set in the extracted positionand the rings 31 and 50.

The locking element 55 is arranged on the axial side of the bearing 17opposite to the mast 6.

In greater detail, the locking element 55 extends annularly about axis Aand comprises (FIGS. 3 to 9):

-   -   a main body 60;    -   a ring 65 axially spaced apart from the main body 60; and    -   a plurality of arms 70 angularly and evenly spaced around axis A        and interposed between the main body 60 and ring 65.

When the locking element 55 is in the standard configuration (FIGS. 4and 5):

-   -   ring 65 is blocked by interference on a surface 38 of ring 31        radially external with respect to axis A; and    -   the arms 70 connect the main body 60 and ring 65.

In this standard configuration, ring 65 prevents the rotation of ring31, due to the radial interference between ring 65 and surface 38.

In particular, ring 65 is also blocked by radial interference on surface38 by the part axially opposite to the mast 6.

In the case shown, ring 65 surrounds and touches surface 38.

Referring to FIGS. 6 and 7, when the locking element 55 is in the firstemergency configuration, ring 65 is disengaged from surface 38 of ring31, which thus becomes free to rotate about axis A integrally with ring30 under the twisting moment improperly transmitted by ring 31.

Referring to FIGS. 8 and 9, when the locking element 55 is in the secondemergency configuration, the arms 70 are interrupted and no longerconnect the main body 60 and ring 65. Even in this second emergencyconfiguration of the locking element 55, ring 31 becomes free to rotateabout axis A integrally with ring 30 under the twisting momentimproperly transmitted by ring 31.

The locking element 55 is made of a material having a first thermalexpansion coefficient, and ring 50 is made of a material having a secondthermal expansion coefficient, lower than the first thermal expansioncoefficient.

The first thermal expansion coefficient is greater than the secondthermal expansion coefficient.

In the case shown, the locking element 55 is made of aluminium and rings30, 31 and 50 are made of steel.

Therefore, in the event of a temperature increase of the bearing 17 dueto its failure that is above the threshold value, ring 65 radiallydilates more than surface 38 of ring 50 until it is radially separatedfrom ring 50.

Once ring 65 leaves surface 38 free, the locking element 55 is arrangedin the first emergency configuration.

The arms 70 are sized so as to break under torsion, when the vibrationsand/or twisting moment transmitted to ring 31 exceed a threshold value.

In this way, the locking element 55 moves from the standardconfiguration to the second emergency configuration (FIGS. 8 and 9),when the vibrations and/or twisting moment transmitted to ring 31 exceeda threshold value.

Furthermore, the arms 70 are angularly and evenly spaced around axis Aand extend parallel to axis A.

The main body 60 also comprises:

-   -   a cylindrical portion 62, from which the arms 70 project axially        in a cantilever fashion; and    -   a collar 61 projecting radially in a cantilever fashion from        portion 62 in a direction opposite to axis A and defining an        axial end of the main body 60 opposite to ring 65.

In the case shown, the diameter of the main body 60 is equal to thediameter of ring 65.

The locking element 55 also comprises a ring 64 arranged axially inabutment against the collar 61 on the side of the bearing 17 andannularly touching the main body 60 on the side opposite to axis A.

The locking element 55 also comprises a plurality of appendages 75extending axially in a cantilever fashion from the main body 60 andaxially set apart from ring 65.

The appendages 75 define respective axial slots 76.

In the case shown, the appendages 75 are U-shaped. The appendages 75also comprise two axial segments 71 projecting in a cantilever fashionfrom the main body 60 and a free connecting segment 72 between the arms71.

In the case shown, segments 72 of the appendages 75 extend fromrespective segments 71, so as to be divergent with respect to axis A,proceeding parallel to axis A in a direction opposite to segments 71.

The appendages 75 are angularly and evenly spaced out from each other.

The appendages 75 and the arms 70 circumferentially variating with oneanother.

The appendages 75 are axially set apart and distinct from ring 65.

In the case shown, ring 65 is arranged axially between the main body 60and the rolling bodies 32.

The anti-torque rotor 4 also comprises:

-   -   a ring 80 connected to ring 50 by a plurality, six in the case        shown, of axial pins 82 angularly and evenly spaced out from        each other, so as to be angularly fixed with respect to axis A        and axially and integrally sliding with ring 50, the bearing 17        and the control rod 10;    -   a ring 85 angularly fixed with respect to axis A and axially and        integrally sliding with ring 50, the bearing 17 and the control        rod 10; and    -   a plurality of pins 81, four in the case shown, of radial        extension, engaging respective slots 76 with axial play,        fastened to ring 80 and arranged in axial abutment against ring        85.

In the case shown, portion 62 of the main body 60 is radially interposedbetween rings 80 and 85.

Referring to FIGS. 3 to 9, ring 80 is fastened to segment 26 of the mainbody 25 and these are axially interposed between a nut 29 screwed on theend 24 of the control rod 10 and the shoulder 28 of the control rod 10.

When arranged in the first or second emergency configuration (FIGS. 6 to9), the locking element 55 can slide along axis A with respect to rings85, 80, 31 and 30 and the control rod 10. This happens because the pins81 engage the respective slots 76 with axial play.

When the locking element 55 is in the standard configuration (FIGS. 4and 5), the pins 81 are arranged in axial abutment against respectiveaxial ends 77 of the corresponding slots 76 arranged on the oppositeside of the bearing 17 (FIG. 5).

Contrariwise, when arranged in the first or second emergencyconfiguration (FIGS. 6 to 9), the locking element 55 can slide up to theextracted position, where the pins 81 are arranged in axial abutmentagainst respective axial ends 78, opposite to ends 77, of thecorresponding slots 76 arranged on the side of the bearing 17 (FIG. 7).

The anti-torque rotor 4 also comprises a spring 100 interposed betweenring 50 and the locking element 55.

The spring 100 is configured to exert an elastic force on the lockingelement 55 directed parallel to axis A and oriented from the oppositeside of the bearing 17. This force elastically preloads the lockingelement 55 towards the extracted position in FIGS. 6 to 9.

This elastic force is countered by the axial friction force opposing it,arising from the radial interference between ring 65 and surface 38,when the locking element 55 is in the inserted position, reached in thestandard configuration (FIGS. 4 and 5).

Once the locking element 55 is arranged in this first or secondemergency configuration, it is axially pushed by the spring 100 from theside opposite to the bearing 17 until it reaches the extracted position(FIGS. 6 to 9).

Reaching this extracted position is indicative of the failure conditionof the bearing 17.

More specifically, the spring 100 is interposed between ring 64 integralwith the locking element 55 and ring 85 in abutment against the pins 81.

In the case shown, the spring 100 is a wave spring.

In particular, the spring 100 comprises two annularly extending waveelements that axially cooperate with each other.

Referring to FIG. 2, the anti-torque rotor 4 also comprises a coverelement 46 fastened to flange 42 and, consequently, rotatable about axisA with element 16.

The cover 46 defines a cavity 47 symmetrical with respect to axis A andhousing the main body 60, the spring 100, the nut 29, the pins 81 andrings 80 and 85.

Preferably, the cover 46 is made of a transparent material and isvisible from outside the helicopter 1.

Cover 46 is rotatable about axis A integrally with control element 16.

The locking element 55 also preferably comprises a coloured annular band(not shown in the accompanying figures).

This annular band is visible from the outside through the cover 46 whenthe locking element 55 is in the extracted position, so as to provide animmediate indication of the fact that the locking element 55 is in theextracted position.

Contrariwise, this annular band is not visible from the outside throughthe cover 46 when the locking element 55 is in the inserted position.

Referring to FIGS. 5, 7 and 9, the shoulder 37 of the bearing 17 isradially set apart from ring 30.

The outer diameter of the shoulder 37 is greater than the inner diameterof the tracks 33 and 34.

Due to this, in the event of failure of the bearing 17 that results inthe destruction of the rolling bodies 32, translation of the control rod10 towards track 33 brings shoulder 37 into abutment against track 33.

Similarly, translation of the control rod 10 towards track 34 bringsshoulder 37 into abutment against track 34.

The condition of contact in the axial direction of shoulder 37 againsttracks 33 and 34 makes the set formed by the control rod and rings 31and 50 again able to slide along axis A integrally with ring 30, therebypreserving the controllability of the anti-torque rotor 4.

Furthermore, the shoulder 37 is axially set apart from the cages 39 ofthe rolling bodies 32.

The bearing 17 also comprises an annular insert 93 axially interposedbetween half-rings 31 and arranged on the radially outer surface of ring30.

The backup bearing 54 also comprises an annular insert 94 interposedbetween half-rings 45 and arranged on the radially inner surface 58 ofring 50.

Operation of the anti-torque rotor 4 is described hereinafter startingfrom a condition (FIGS. 2, 4 and 5) in which the bearing 17 functionscorrectly and the locking element 55 is arranged in the standardconfiguration and in the inserted position.

In this condition, operation of the flight control 15 causes translationof the control rod 10 in a given direction along axis A.

This translation causes integral translation of the bearing 17 andelement 16 along axis A.

Consequently, element 16 moves away from (or closer to) the blades 8 andvaries the inclination of the levers 43 with respect to axis B,increasing (or decreasing) the angle of attack of the blades 8.

This movement of the levers 43 causes the simultaneous rotation by equalangles of the blades 8 about the associated axes B and the consequentadjustment of the angles of attack of the blades 8.

The bearing 17 enables rotation of element 16 with respect to thecontrol rod 10 about axis A.

In greater detail, ring 30 rotates integrally with element 16 about axisA and rings 31 and 50 remain fixed with respect to axis A.

This happens because ring 65 is pressed on ring 31 with radialinterference, preventing rotation of the latter and, consequently, alsoof ring 50.

Axial friction force generated by this interference assembly is greaterthan the elastic force applied by the spring 100 on the locking element55.

In this condition, ring 50, and consequently the backup bearing 54, aresubstantially inactive.

In the event of failure of the bearing 17, that results in an increasein temperature in the area of the bearing 17 above a respectivethreshold value, the radial thermal dilation of ring 65 is greater thanthe thermal dilation of ring 31.

Consequently, the locking element 55 moves to the first emergencyconfiguration (FIGS. 6 and 7), in which ring 65 is set apart from ring31.

Ring 31 can thus rotate about axis A with respect to ring 50, whichinstead remains angularly fixed about axis A, as it is blocked on thecontrol rod 10.

In this condition, ring 31 and the bearing 17 are substantially inactiveand the rotation of element 16 with respect to the control rod 10 aboutaxis A is enabled by the backup bearing 54.

In the event of failure of the bearing 17 that results in an increase inthe torque transmitted from ring 31 to ring 30 and/or in the vibrationsin the area of the bearing 17 above respective threshold values, thetorsional breakage of the arms 70 is induced.

This breakage places the locking element 55 in the second emergencyconfiguration (FIGS. 8 and 9).

Similarly to the first emergency configuration, ring 31 can thus rotateabout axis A with respect to ring 50, which instead remains angularlyfixed about axis A.

Furthermore, ring 31 and the bearing 17 are substantially inactive andthe rotation of element 16 with respect to the control rod 10 about axisA is enabled by the backup bearing 54.

Once set in the first or second configuration, the locking element 55 ispushed by the spring 100 towards the extracted position (FIGS. 6 to 9).

This sliding causes the movement of the slots 76 with respect to thepins 81 and ring 85.

In the extracted position, the annular band of the locking element 55 isvisible from outside the helicopter 1, visually informing the pilot orinspection engineer that the bearing 17 is in an incipient or effectivefailure condition.

In the event of failure of the bearing 17 that results in thedestruction of the rolling bodies 32, the translation of the control rod10 towards track 33 (34) brings shoulder 37 into abutment against track33 (34), maintaining two-way axial contact between the control rod 10and the bearing 17, thereby ensuring the controllability of theanti-torque rotor 4.

With reference to FIGS. 12 and 13, reference numeral 4′ indicates ananti-torque rotor according to a second embodiment of the presentinvention.

Rotor 4′ is similar to rotor 4 and only the differences from the latterwill be described hereinafter; identical or equivalent parts of therotor 4, 4′ will be marked, where possible, with the same referencenumerals.

Rotor 4′ differs from rotor 4 for not comprising shoulder 37.Furthermore, rotor 4′ differs from rotor 4 for comprising a pair ofblocking elements 90′ axially interposed between shoulders 35, 36.

Rotor 4′ also differs from rotor 4 in that surface 38′ comprises a pairof stretches 99′ axially interposed between rolling bodies 32.

Stretches 99′ are axially consecutive and symmetrically converge towardsone another on the opposite side of axis A with respect to therespective remaining parts of surface 38′.

Stretches 99′ are planar, so as to define a chevron towards blockingelements 90′.

Blocking elements 90′ are fixed to ring 30.

In the normal configuration, bearing 17 does not allow any axialmovement between rings 30, 31.

In this normal configuration, blocking elements 90′ integrally rotatewith ring 30 with respect to ring 31.

Furthermore, blocking elements 90′ are spaced by respective stretches99′ by means of respective clearances 108′. Differently, in the event ofdamage of tracks 33, 34 of rolling bodies 32—this phenomenon is known inthe art as “spalling”—, a certain axial movement is allowed betweenrings 30, 31.

In this condition, blocking elements 90′ engage with contact respectivesurfaces 99′, thus substantially reducing or even substantiallypreventing the wear between rings 30, 31.

In greater detail, blocking elements 90′ are axially interposed betweenrolling bodies 32.

Each blocking element 90′ comprises a respective radially inner surface101′ tapered with respect to axis A.

Furthermore, each blocking element 90′ is bound by a respective radiallyouter surface 102′ radially opposite to respective inner surface 101′with respect to axis A.

The size of surface 101′ parallel to axis is greater than surface 102′parallel to axis A.

Each element 90′ is further bound by a respective radial surface 103′,which extends between and is in contact with respective surfaces 101′,102′.

Each element 90′ also comprises:

-   -   a respective main body 105′ defining surfaces 101′, 102′, 103′;    -   a respective radial shoulder 106′, which protrudes from body        105′ and is bound by surfaces 102′, 103′; and    -   a further respective radial shoulder 107′, which protrudes from        body 105′, is axially spaced from respective shoulder 106′ and        bounds blocking element 90′ on the axial opposite side with        respect to respective surface 103′.

The radial size of shoulder 106′ relative to axis A is larger than theradial size of shoulder 107′ relative to axis A.

Shoulder 106′ of each blocking element 90′ is axially interposed betweenrespective shoulder 107′ and surface 103′.

Blocking elements 90′, respective clearances 108′ and respectivesurfaces 101′ are symmetrically arranged with respect to a planeorthogonal to axis A.

In particular, surfaces 103′ of respective elements 90′ axially abutagainst one another parallel to axis A and lie on a plane orthogonal toaxis A.

Surfaces 101′ symmetrically diverge from one another proceeding andtowards axis A starting of respective surfaces 103′ towards respectiveshoulders 107′.

Clearances 108′ diverge from one another starting of respective surfaces103′ towards respective shoulders 107′.

Shoulders 106′ and 107′ contact respective half-rings 41 of ring 30.

Still more precisely, shoulders 106′ are axially interposed betweenhalf-rings 41.

Shoulders 107′ radially abut against radially inner surfaces 109′ ofrespective half-rings 41.

The operation of rotor 4′ differs from the operation of rotor 4 in thatblocking elements 90′ rotate with ring 30 about axis A relative tostationary ring 31 and are spaced from relative stretches 99′ by meansof relative clearances 108′, when bearing 17 correctly operates andlocking element 55 is in the standard configuration and in the insertedposition.

In this condition, bearing 17 substantially prevents any axial movementbetween rings 30, 31.

Differently, in the event of failure of bearing 17 due to damage oftracks 33, 34 of rolling bodies 32—this phenomenon is known in the artas “spalling”—, a certain axial movement might be allowed between rings30, 31.

However, in this condition, blocking elements 90′ block against relativestretches 99′ of ring 31, thus preventing this axial movement and theresulting wear, heat generation and potential damage of rings 30, 31.

In particular, the axial displacement of ring 31 is caused by themovement of control rod 10 due to the pilot action.

With reference to FIGS. 14 to 17, reference numeral 4″ indicates ananti-torque rotor according to a third embodiment of the presentinvention.

Rotor 4″ is similar to rotor 4 and only the differences from the latterwill be described hereinafter; identical or equivalent parts of therotor 4, 4″ will be marked, where possible, with the same referencenumerals.

Rotor 4″ differs from rotor 4 in that rings 50″, 31″ and rolling bodies51″ form bearing 17″.

Differently, rings 31″, 30″ and rolling bodies 32″ form back-up bearing54″.

In the embodiment shown, rolling bodies 51″ roll on respective tracks52″, 53″ of respective rings 31″, 50″. Furthermore, rolling bodies 51″form two axially spaced rings of tapered rollers.

Rolling bodies 51″ are, in the embodiment shown, axially pre-loaded andare tapered rollers.

Rolling bodies 32″ roll on respective tracks 33″, 34″ of respectiverings 30″, 31″. In the embodiment shown, rolling bodies 32″ form twoaxially spaced rings of tapered rollers. Rolling bodies 32″ are, in theembodiment shown, axially pre-loaded and axially interposed betweenrolling bodies 51″. Radially outer surface 57″ of ring 50″ comprises apair of stretches 98″ defining respective tracks 53″ and a pair ofstretches 99″ axially interposed between stretches 98″.

Stretches 99″ are axially consecutive and symmetrically converge towardsone another on the side of axis A with respect to the remaining part ofsurface 57″.

Stretches 99″ are planar, so as to define a chevron.

Ring 31″ comprises, in turn:

-   -   a central body 120″; and    -   a pair of lateral protrusions 101″ axially opposite to another        and protruding from respective opposite axial sides of body        120″.

Body 120″ is bound by a pair or radially inner surfaces 103″, whichconverge towards one another on the side of axis A and face respectivestretches 99″.

In detail, surfaces 103″ are radially external with respect to relativestretches 99″.

When bearing 17″ correctly operates and locking element 55″ is in thestandard configuration and in the inserted position, surfaces 103″ areseparated from respective stretches 99″ of ring 50″ by respectiveclearances 108″.

Surfaces 103″, clearances 108″ and stretches 99″ symmetrically extendwith respect to a plane orthogonal to axis A.

Differently, in the event of failure of bearing 17″ due to damage oftracks 52″, 53″ of rolling bodies 51″—this phenomenon is known in theart as “spalling”—, a certain axial movement might be allowed betweenrings 50″, 31″.

However, in this condition, surfaces 103″ axially block against relativestretches 99′ of ring 31″, thus preventing this axial movement and theresulting wear, heat generation and potential damage of rings 50″, 31″.

Protrusions 101″ define, on respective radially outer surfaces,respective tracks 34″ and, on respective radially inner surfaces,respective tracks 52″.

Rotor 4″ also differs from rotor 4 in that, when arranged in thestandard configuration and in the inserted position shown in FIGS. 14and 16, locking element 55″ prevents the relative rotation of rings 30″,31″ and allows the relative rotation between the assembly formed byrings 30″, 31″ and stationary ring 50″, when bearing 17″ is in normaloperative condition. In this condition, ring 50″ is angularly stationarywith respect to axis A whereas ring 31″, 30″ rotate about axis A. Insuch condition, the rotation among rings 50″ and 30″, 31″ could belubricated by grease.

Furthermore, locking element 55″, when set arranged in the first orsecond emergency configuration and in the extracted position shown inFIGS. 15 and 17, renders rings 31″, 50″ integral to one another aboutaxis A and allows the rotation of ring 30″ about axis A and relative tothe stationary assembly formed by rings 31″, 50″, when bearing 17″ is inthe failure condition.

Accordingly, when bearing 17″ is in the failure condition, rings 50″,31″ are angularly stationary with respect to axis A whereas ring 30″rotate about axis A.

In this condition, rings 31″, 30″ define back-up bearing 54″. Lockingelement 55″ differs from locking element 55 for rotating about axis Aintegrally together with spring 100 and cover 46.

In particular, locking element 55″ comprises a plurality of pins 81″similar to pins 81 integrally rotating with cover 46 and engaging withan axial play respective slots 76″ similar to slots 76 integrallyrotating with cover 46.

Rotor 4″ further differs from rotor 4 for advantageously comprising:

-   -   a tank 150″ filled with a lubricant fluid;    -   a breakable element 151″ which bounds tank 150″ on the side of        rings 30″, 31″, 50″; and    -   a plurality of punching elements 152″ carried by locking        elements 55″;

punching elements 152″ are spaced from breakable element 151″, whenlocking element 55″ is in the inserted position (FIGS. 14 and 16), andpunch breakable element 151″ when locking element 55″ is in theextracted position (FIGS. 15 and 17).

Breakable element 151″ fluidly isolates tank 150″ and rolling bodies 32″when locking element 55″ is in the inserted position (FIGS. 14 and 16),and fluidly connects tank 150″ and rolling bodies 32″ when lockingelement 55″ is in the extracted position (FIGS. 15 and 17).

In detail, tank 150″ is defined by cover 46 and extends annularly aboutaxis A.

Breakable element 151″ extends parallel to axis A and closes tank 150″on the opposite side of cover 46, when locking element 55″ is in theinserted position.

In the embodiment shown, breakable elements 151″ is a discoidalmembrane, preferably made of Aluminum.

Punching elements 152″ protrude from body 60 of locking elements 55″ onthe axial opposite side with respect to ring 65.

In the embodiment shown, punching element 152″ are angularly spacedabout axis A.

As shown in FIG. 15, punching elements 152″ are shaped as relativelances with convergent shaped sharp tips, proceeding from body 60towards breakable element 151″.

Preferably, punching elements 152″ are radially outer with respectelement 65 and define a radially outer periphery of element 55″.

In the embodiment shown, body 60 and punching elements 152″ are made ofTitanium.

Ring 65 and arms 70 are made of Aluminum, in the embodiment shown.

When locking element 55″ is in the extracted position shown in FIG. 17,rotor 4″ defines a fluidic path 170″ from tank 150″ to a region 160″surrounding rolling bodies 32″.

In detail, region 160″ is radially bound between rings 30″, 31″.

Region 160″ is axially bound between shoulders 35, 36 on the oppositeradial side with respect to axis A and between protrusions 101″ on theside of axis A.

With reference to FIG. 17, fluidic path 170″ extends at radial peripheryof rotor 4″. Furthermore, path 170″ comprises a plurality of throughopenings 171″ axially extending through broken elements 152″, a passage175″ between rings 65, 31 and a passage 176″ between rings 31″, 30″.

Differently, when locking element 55″ is in the extracted position shownin FIG. 17, fluidic path 170″ is interrupted by breakable element 151″.

Rotor 4″ also comprises a labyrinth seal 180″ arranged on the oppositeaxial side of rolling bodies 32″ with respect to breakable element 102″and adapted to tight close fluidic path 170″ and to keep lubricant fluidin continuous contact with rolling bodies 32″, when locking element 55″is in the extracted position.

In detail, labyrinth seal 180′ comprises (FIG. 17):

-   -   a seal 181″ radially interposed between rings 50″, 31″ on the        opposite axial side with respect to element 55″; and    -   a seal 182″ radially interposed between rings 50″, 30″ on the        opposite axial side of seal 181″ with respect to rolling bodies        32″.

In particular, seals 181″, 182″ are shaped as annuluses. Seal 182″ has aradial size greater than seal 181″, in the embodiment shown.

The operation of rotor 4″ differs from the operation of rotor 4 in thatlocking element 55″ integrally rotates with cover 46 and ring 30″ aboutaxis A, thanks to the connection between the pins and the respectiveslots.

When the locking element 55″ is in the inserted position and in thestandard configuration of FIGS. 14 and 16, bearing 17″ formed by rings50″, 31″ and rolling bodies 51″ enables rotation of element 16 withrespect to rod 10 about axis A.

In greater detail, ring 50″ is stationary about axis A and rings 31″,30″ rotate integrally about axis A. In this condition, locking element55″ is in contact with ring 31″ and angularly integral with ring 31″.

Furthermore, back-up bearing 54″ is substantially inactive.

Punching elements 152″ are spaced from breakable element 151″, which isstill unbroken.

Accordingly, lubricant fluid remains in tank 150″ In the event offailure of bearing 17″ which results in an increase in the temperatureof bearing 17″ above the threshold value or in an increase of the torquetransmitted from ring 31″ to ring 50″ and/or in the vibrations in thearea of bearing 17″ above respective values, locking element 55″ isdisplaced in the first or second emergency configuration shown in FIGS.15 and 17.

Accordingly, spring 100 displaces locking element 55″ in the extractedposition shown in FIGS. 15 and 17.

In this condition, ring 31″ remains angularly stationary and rollingbodies 32″ allow the rotation of ring 30″ relative to ring 31″ and aboutaxis A.

Furthermore, punching elements 152″ break breakable element 151″. Inthis way, the lubricant fluid contained in tank 150″ can flow alongfluidic path 170″ from tank 150″ to region 160″ and ensure a continuouslubrication of rolling bodies 32″.

More precisely, lubricant fluid flow through passages 171″ throughbroken breakable element 151″ and through passage 172″ between rings 65,31″.

The rotation of locking element 55″, cover 45 and rings 31″, 30″generates, for centrifugal action, a lubricant fluid bath (shown in greyin FIG. 17) in the peripheral region of rotor 4″ whereat rolling bodies32″ are arranged, as shown in FIG. 17.

Labyrinth seal 180″ is effective in containing the lubricant fluid inregion 160″

Regardless the configuration of locking element 55″, normal blockingsurfaces 103″ rotate with ring 31″ about axis A relative to stationaryring 50″ and are spaced from relative stretches 99″ by means of relativeclearances 108″.

In this condition, bearing 17″ substantially prevents any axial movementbetween rings 50″, 31″.

Differently, in the event of failure of bearing 17″ due to damage oftracks 53″, 52″ of rolling bodies 51″—this phenomenon is known in theart as “spalling”—, a certain axial movement might be allowed betweenrings 50″, 31″.

However, in this condition, surfaces 103″ of ring 31″ block againstrelative stretches 99″ of ring 50″, thus preventing this axial movementand the resulting wear, heat generation and potential damage of rings50″, 31″.

From an examination of the characteristics of the anti-torque rotor 4,4′, 4″ according to the present invention, the advantages that can beachieved therewith are evident.

In greater detail, the locking element 55 prevents the relative rotationof rings 31 and 50 in the standard configuration (FIGS. 4 and 5), andenables the rotation of ring 31 with respect to ring 50 in the first andsecond emergency configurations (FIGS. 6 to 9), when the bearing 17 isin incipient or effective failure.

In this way, in the event of incipient or effective failure that resultsin the seizing, even if only partial, of the bearing 17, rings 30 and 31rotate integrally with one another with respect to ring 50, thusallowing to preserve the possibility of regulating the angles of attackof the blades 8 via the control rod 10. In other words, in the event offailure, the bearing 17 becomes inactive and the backup bearing 54 isautomatically activated.

In greater detail, in the case of increased temperature in the area ofthe bearing 17, the locking element 55 moves from the standardconfiguration to the first emergency configuration.

More specifically, by having a larger thermal dilation coefficient, ring65 disengages from surface 38 of ring 31, which has a lower thermaldilation coefficient.

In the case where the torque acting on ring 31 or the vibrations in thearea of the bearing 17 exceed the respective threshold values, thelocking element 55 moves from the standard configuration to the secondemergency configuration.

More specifically, the arms 70 break under torsion.

In this way, rings 31 and 30 rotate with respect to ring 50, when thetemperature in the area of the bearing 17 exceeds the respectivethreshold value and/or when the torque improperly acting of ring 31 orthe vibrations in the area of the bearing 17 exceed the respectivethreshold values.

Furthermore, the locking element 55 is arranged in the extractedposition when it reaches the first or second standard configuration.

In this way, it is possible to recognise the incipient or effectivestate of failure of the bearing 17 simply on the basis of the axialposition of the locking element 55 with respect to the control rod 10.

The spring 100 elastically preloads the locking element 55 towards theextracted position, favouring reaching this position quickly.

When the locking element 55 is in the extracted position, the band isvisible from outside the helicopter 1 to the crew and/or inspectionengineers through the transparent cover 46, thereby providing a clearand immediate indication that the bearing 17 is in a failure condition.

The shoulder 37 has an outer diameter greater than tracks 33 and 34 ofthe bearing 17.

Due to this, in the event of failure of the bearing 17 that results inthe destruction of the rolling bodies 32, translation of the control rod10 towards track 33 or 34 brings shoulder 37 into abutment against track33 or 34, preserving the controllability of the anti-torque rotor 4, 4′.

Rotor 4′ (FIGS. 12 and 13) further comprises a pair of blocking element90′ carried by ring 30 and provided with respective tapering surfaces101′.

Surfaces 101′ are spaced from respective stretches 99′ of ring 31, whenbearing 17 is in the normal operative condition.

Differently, surfaces 101′ block blocking elements 90′ integral withring 30 against respective stretches 99′ of ring 31 in the event offailure of bearing 17 due to damage of tracks 33, 34 of rolling bodies32.

In this way, also when tracks 33, 34 are damaged, any relative axialmovement between rings 30, 31 is substantially prevented. Accordingly,the risk of wear of heat generation and resulting damage of rings 30, 31is substantially avoided.

Locking element 55″ of rotor 4″ allows the relative rotation of ring 31″relative to ring 50″ in the standard configuration (FIGS. 14 and 16),and enables the relative rotation of ring 30″ with respect to ring 31″in the first and second emergency configurations (FIGS. 15 to 17), whenthe bearing 17″ is in incipient or effective failure.

In this way, locking element 55″ of rotor 4″ achieves substantially thesame advantages as locking element 55 of rotor 4.

Furthermore, locking element 55″ comprises a plurality of punchingelements 152″, which break breakable elements 151″, when locking element55″ is set in the extracted position and in case of failure of bearing17″.

In this way, the lubricant fluid contained in tank 150″ can flow alongfluidic line 170″ towards rolling bodies 32″ and ensure their properoperation of back-up bearing 54″.

The rotation of cover 46, locking element 55″ and ring 30″ about axis Athrusts, for centrifugal action, the lubricant fluid towards rollingbodies 32″ which are arranged radially outer than rolling bodies 51″.

In this way, the centrifugal action generates a lubricant fluid bath inthe peripheral region of rotor 4″ whereat rolling bodies 32″ and region160″ are arranged.

Labyrinth seal 180″ is effective in containing the lubricant fluid inregion 160″.

Similarly to rotor 4′, surfaces 103″ of ring 31″ are spaced fromrespective stretches 99″ of ring 30″, when bearing 17″ is in the normaloperative condition.

Differently, surfaces 103″ block against respective stretches 99″ in theevent of failure of bearing 17″ due to damage of tracks 52, 53 ofrolling bodies 51″.

In this way, also tracks 52, 53 of rolling bodies 51″ are damaged, anyaxial relative movement between rings 50″, 31″ is substantiallyprevented.

Accordingly, the risk of wear of heat generation and resulting damage ofrings 50″, 31″ is substantially avoided.

Rings 30, 30″; 31, 31″; 50, 50″ of rotors 4, 4′, 4″ are coaxial andextends about common axis A.

Still more precisely, rings 50, 50″ are radially inner with respect torings 31, 31″, which are, in turn, radially inner with respect to rings30, 30″.

Accordingly, bearing 17, 17″; 54, 54″ of rotor 4, 4′, 4″ areparticularly compact radially to axis A in comparison with the solutionshown in U.S. Pat. No. 9,359,073 and discussed in the introductory partof the present description.

In this way, tracks 52″, 53″, 33″, 34″ can be coaxially mounted insiderotor 4, 4′, 4″ with a very limited axial size, thus renderingsubstantially unnecessary any re-design of rotor 4, 4″ differently fromthe solution shown in U.S. Pat. No. 9,359,073.

Furthermore, tracks 52″, 53″, 33″, 34″ are defined by only three rings30, 30″; 31, 31″; 50, 50″, instead of the four rings disclosed in U.S.Pat. No. 9,359,073.

Being rings 30, 30″; 31, 31″; 50, 50″ coaxial, bearing 17, 17″, 54, 54″are capable of transmitting translation loads along a first directionparallel to axis A and a second and a third direction orthogonal to axisA as well as rotational loads about the second and the third direction.

Differently, the bearings disclosed in U.S. Pat. No. 9,359,073 areeffective to transmit only axial load parallel to the rotation directionof the mast.

Furthermore, bearing 17, 17″; 54, 54″ comprise two rings of rollingbodies 32, 32″; 51, 51″.

In this way, rolling bodies 32, 32″; 51, 51″ can be easily axiallypre-loaded, thus strongly containing the axial play and the resultingvibrations and noise.

Rolling bodies 51, 51″ are conical roller. In this way, bearing 17, 17″;54, 54″ are substantially not exposed to false brinelling damagemechanism.

Finally, it is clear that modifications and variants can be made withregard to the anti-torque rotor 4, 4′, 4″ described and illustratedherein without departing from the scope defined by the claims.

In particular, ring 50 could be arranged radially external to ring 30.

Moreover, the locking element 55 could comprise a plurality of radialpins interposed between ring 65 and surface 38. These pins would bebreakable if the torque transmitted from ring 30 to ring 31 and/or thevibrations in the area of the bearing 17 exceed the respective thresholdvalues. These pins would also be made of a material having aparticularly low torsional resistance above the threshold value.

The locking element 55 could also comprise brazing between rings 31 and50 and sized so as to enable rotation between rings 31 and 50 when thetorque transmitted from ring 30 or the vibrations in the area of thebearing 17 exceed the respective threshold values. Furthermore, thebrazing would be made using a material that would enable rotation ofring 31 with respect to ring 50 upon exceeding the temperature thresholdvalue.

The rolling bodies 32, 32″ and 51, 51″ could also be needle rollers,spherical rollers, self-aligning ball bearings, or plain ball bearings.

The rolling bodies 32, 32″ and 51, 51″ could also have a “0” (back toback) arrangement instead of a “X” (face to face) arrangement.

1. An anti-torque rotor (4′) for a helicopter (1), comprising: a mast(6), rotatable about a first axis (A); a plurality of blades (8), hingedon said mast (6), extending along respective second axes (B) transversalto said first axis (A) and rotatable about respective said second axes(B) to vary the respective angles of attack; an element (16), slidingalong said first axis (A) with respect to said mast (6), integrallyrotating with said mast (6), and operatively connected to said blades(8) to cause the rotation of said blades (8) about respective saidsecond axes (B) following a translation of said element (16) along saidaxis (A); a control rod (10), sliding axially along said first axis (A)with respect to said mast (6) and angularly fixed with respect to saidfirst axis (A); and a first bearing (17) interposed between said controlrod (10) and said element (16), sliding along said first axis (A) withrespect to said mast (6) and integrally with said control rod (10), andconfigured to enable the relative rotation of said element (16) withrespect to said control rod (10) about said first axis (A) in a normaloperating condition; said first bearing (17), in turn, comprising: afirst ring (30) rotatable integrally with said element (16) about saidfirst axis (A); a second ring (31) radially internal to said first ring(30) with respect to said first axis (A) and sliding integrally withsaid control rod (10) along said first axis (A); a plurality of firstrolling bodies (32), which are interposed between said first and secondrings (30, 31) and adapted to roll on respective first tracks (33, 34)of said first and second rings (30, 31); said rotor (4) furthercomprising: a third ring (50) slidable integrally with said control rod(10) along said first axis (A) and angularly fixed with respect to saidfirst axis (A); a plurality of second rolling bodies (51), which areinterposed between said second and third rings (31, 50) and are adaptedto roll on respective second tracks (52, 53) of said second and thirdrings (31, 50); and a locking element (55) arranged in a standardconfiguration, wherein it prevents the relative rotation of said secondand third rings (31, 50), when said first bearing (17) is, in use, in anormal operating condition; said locking element (55) being movable fromsaid standard configuration to at least a first or second emergencyconfiguration, wherein it makes said second ring (31) free to rotatewith respect to said third ring (50) about said axis (A), when saidfirst bearing (17) is, in use, in a failure condition; characterized inthat said second ring (31) comprises a radially outer surface (38′) withat least one tapered stretch (99′) axially interposed between said firstrolling bodies (32); said first ring (30) comprising at least oneblocking element (90′) with at least one tapered first surface (101′)radially facing said stretch (99′) and separated with a clearance (108′)by said stretch (99′), when said first bearing (17) is, in use, in saidnormal operation.
 2. The anti-torque rotor of claim 1, characterized inthat said at least one blocking element (90′) is axially blocked againstsaid at least one stretch (99′), in case of damage of said first tracks(33, 34) of said rolling bodies (32).
 3. The anti-torque rotor of claim1, characterized in that said blocking element (90′) is fixed to saidfirst ring (30).
 4. The anti-torque rotor of claim 1, characterized inthat said at least one first surface (101′) and said at least onestretch (99′) are parallel to one another.
 5. The anti-torque rotor ofclaim 1, characterized in that said at least one blocking element (90′)comprises: a radially outer second surface (102′) radially opposite withrespect to said first axis (A) and radially opposite to said firstsurface (101′); and a radial third surface (103′) which extends betweensaid first and second surface (101′, 102′).
 6. The anti-torque rotor ofclaim 5, characterized said at least one blocking element (90′) furthercomprises: a main body (105′) defining said first, second and thirdsurfaces (101′, 102′, 103′); a first radial shoulder (106′), whichprotrudes from said body (105′) and is radially bound by said secondsurface (102′) and third surface (103′); and a second radial shoulder(107′), which protrudes from said body (105′), is axially spaced fromrespective first radial shoulder (106′) and bounds the said blockingelement (90′) on the axial opposite side with respect to said thirdsurface (103′).
 7. The anti-torque rotor of claim 1, characterized bycomprising: a pair of said blocking elements (90′) with respective saidfirst surfaces (101′) and in axial contact with one another; a pair ofsaid first stretches (99′) associated to respective said blockingelements (90′); and a pair of said clearances (108′) interposed each,between a respective said stretch (99′) and a respective first surface(101′) of a respective said blocking element (90′).
 8. The anti-torquerotor of claim 7, characterized in that said blocking elements (90′) aresymmetrically mounted with respect to a plane orthogonal to said firstaxis (A).
 9. The anti-torque rotor of claim 7, characterized in thatsaid first surfaces (101′) converge towards one another on the oppositeside of said first axis (A).
 10. The anti-torque rotor of claim 7,characterized in that said third surfaces (103′) of respective saidblocking elements (90′) axially abut against one another.
 11. Theanti-torque rotor of claim 6, characterized in that said first radialshoulders (106′) are axially interposed between respective half-rings(41) of said first ring (30); said second radial shoulders (107′) beingin radial contact against said half-rings (41).
 12. The anti-rotor ofclaim 7, characterized in that said blocking elements (90′) areinterposed between said first rolling bodies (32).
 13. An anti-torquerotor (4″) for a helicopter (1), comprising: a mast (6), rotatable abouta first axis (A); a plurality of blades (8), hinged on said mast (6),extending along respective second axes (B) transversal to said firstaxis (A) and rotatable about respective said second axes (B) to vary therespective angles of attack; an element (16), sliding along said firstaxis (A) with respect to said mast (6), integrally rotating with saidmast (6), and operatively connected to said blades (8) to cause therotation of said blades (8) about respective said second axes (B)following a translation of said element (16) along said axis (A); acontrol rod (10), sliding axially along said first axis (A) with respectto said mast (6) and angularly fixed with respect to said first axis(A); a first ring (30″) rotatable integrally with said element (16)about said first axis (A); a second ring (50″) slidable integrally withsaid control rod (10) along said first axis (A); a third ring (31″); aplurality of first rolling bodies (51″), which are interposed betweensaid second and third rings (50″, 31″) and adapted to roll on respectivefirst tracks (52″, 53″) of said second and third rings (50″, 31″); and aplurality of second rolling bodies (32″), which are interposed betweensaid first and third ring (30″, 31″) and adapted to roll on respectivefirst tracks (33″, 34″) of said first and third ring (30″, 31″); saidfirst tracks (52″, 53″) and said first rolling bodies (51″) defining afirst bearing (17″); said rotor (4″) further comprising: a lockingelement (55″) arranged in a standard configuration, wherein it preventsthe relative rotation of said first and third ring (30″, 31″) and allowsthe relative rotation between an assembly formed by said third ring(31″) and said first ring (30″) with respect to said second ring (50″),when said first bearing (17″) is, in use, in a normal operatingcondition; said second ring (50″) being angularly stationary withrespect to said first axis (A) whereas said first and third ring (31″,30″) rotate, in use, about said first axis (A), when said first bearing(17″) is, in use, in said normal operating condition; said lockingelement (55) being movable from said standard configuration to at leasta first or second emergency configuration, when said first bearing (17)is, in use, in a failure condition; said locking element (55″), whenarranged, in use, in said standard configuration, being fastened on saidthird ring (31″); said locking element (55″) being slidable with respectto said third ring (31″) parallel to said first axis (A) between: aninserted position, reached in said standard configuration and whereinsaid locking element (55″) is at a first axial distance from said thirdring (31″); and an extracted position, reached in said first or secondemergency configuration, and wherein said locking element (55″) is at asecond axial distance from said third ring (31″), greater than saidfirst axial distance; characterized in that said rotor (4″) comprises: atank (150″) fillable with a lubricant fluid; and a breakable element(151″) which bounds said tank (150″); said locking element (55″)comprising at least one punching element (152″); said punching element(152″) being spaced from said breakable element (151″), when saidlocking element (55″) is arranged in said inserted position; saidpunching element (152″) punching, in use, said breakable element (151″),when said locking element (55″) is arranged in said extracted position;said breakable element (152″) fluidly isolating said tank (150″) andsaid second rolling bodies (32″) when said locking element (55″) isarranged in said inserted position, and fluidly connecting said tank(150″) with said second rolling bodies (32″) when said locking element(55″) is arranged in said extracted position.
 14. The rotor of claim 13,characterized by comprising elastic means (100) interposed, at leastindirectly, between said second ring (50″) and said locking element(55″); said elastic means (100) elastically preloading said lockingelement (55″) towards said extracted position.
 15. The rotor of claim13, characterized in that said second ring (50″) is radially inner withrespect to said third ring (31″); said third ring (31″) being radiallyinner with respect to said first ring (30″).
 16. The rotor of claim 13,characterized in that said first rolling bodies (51″) and/or said secondrolling bodies (32″) are shaped as tapered rollers.
 17. The rotor ofclaim 13, characterized by comprising: two axially spaced first sets ofsaid first rolling bodies (32″) axially loaded towards one another; andtwo axially spaced second sets of said second rolling bodies (51″)axially pre-loaded towards one another.
 18. The rotor of claim 17,characterized in that said two first sets of first rolling bodies (32″)are axially interposed between said two second sets of said firstrolling bodies (51″).
 19. The rotor according to claim 14, characterizedin that said locking element (55″) and said tank (150″) are rotatableintegrally with said first ring (30″) about said first axis (A), whensaid locking element (55″) is, in use, in said inserted position. 20.The rotor of claim 14, characterized in that said locking element (55″),in turn, comprises: a main body (60) from which said punching element(152″) protrudes towards said breakable element (151″); a fourth ring(65) fastened on said third ring (31″) at least when said lockingelement (55″) is arranged, in use, in said standard configuration; atleast one connection arm (70) interposed between said main body (60) andsaid fourth ring (65), at least when said locking element (55″) isarranged, in use, in said standard configuration; said fourth ring (65)and said connection arms (70) protruding from said main body (60) on theaxial opposite side with respect to said punching element (152″). 21.The rotor of claim 20, characterized in that said main body (60) is madeof Titanium, and in that said fourth ring (65) is made of Aluminium. 22.The rotor of claim 20, characterized in that at least said fourth ring(65) is made of a material having a first thermal expansion coefficientgreater than a second thermal expansion coefficient of said third ring(31″); said fourth ring (65) being disengaged from said third ring(31″), when said locking element (55″) is in said first emergencyconfiguration, reached when the temperature of said first bearing (17″)exceeds, in use, a first threshold value.
 23. The rotor according toclaim 20, characterized in that said main body (60) and said fourth ring(65) are separated from one another, when said locking element (55″) isin a second emergency configuration, reached at least when the torqueacting, in use, on said third ring (31″) exceeds a second thresholdvalue.
 24. The rotor according to claim 23, characterized in that saidarm (70) is breakable when said torque acting, in use, on said thirdring (31″) and on said fourth ring (65) is greater than said secondthreshold value, so as to arrange said locking element (55″) in saidsecond emergency configuration; and/or characterized in that said fourthring (65) is force-fitted by interference on said third ring (31″), whensaid locking element (55″) is arranged, in use, in said standardconfiguration.
 25. The rotor of claim 14, characterized by comprising alabyrinth seal (180″) radially interposed between said second ring (50″)and said third ring (31″) and between said second ring (50″) and saidfirst ring (30″) on the axial opposite side of said tank (150″) withrespect to said second rolling bodies (32″), in order to keep saidlubricant in constant with said rolling bodies (32″) when said lockingelement (55″) is, in use, in said extracted position.
 26. The rotor ofclaim 14, characterized by comprising a fluidic path (170″) extendingbetween said tank (150″) and said second rolling bodies (32″), when saidlocking element (55″) is set in said extracted position; said fluidicpath (170″) comprising a first passage (171″) between said brokenbreakable element (152″) and a second passage (172″) between saidlocking element (55″) and said third ring (31″).
 27. The rotor of claim14, characterized in that third second ring (31″) comprises at least oneradially tapered inner surface (103″) axially interposed between saidfirst rolling bodies (51″); said second ring (50″) comprising at leastone tapered stretch (99″) radially facing said surface (103″) andseparated with a clearance (108″) by said surface (103″) in said normaloperation of said first rolling bodies (51″).
 28. An anti-torque rotor(4; 4′; 4″) for a helicopter (1), comprising: a mast (6), rotatableabout a first axis (A); a plurality of blades (8), hinged on said mast(6), extending along respective second axes (B) transversal to saidfirst axis (A) and rotatable about respective said second axes (B) tovary the respective angles of attack; an element (16), sliding alongsaid first axis (A) with respect to said mast (6), integrally rotatingwith said mast (6), and operatively connected to said blades (8) tocause the rotation of said blades (8) about respective said second axes(B) following a translation of said element (16) along said axis (A); acontrol rod (10), sliding axially along said first axis (A) with respectto said mast (6) and angularly fixed with respect to said first axis(A); a first ring (30; 30″) rotatable integrally with said element (16)about said first axis (A); a second ring (50; 50″) sliding integrallywith said control rod (10) along said first axis (A) and angularly fixedwith respect to said first axis (A); and a third ring (31; 31″); aplurality of first rolling bodies (32; 32″), which are interposedbetween said first and third rings (30, 30″; 31, 31″) and adapted toroll on respective first tracks (33, 34; 33″, 34″) of said first andthird rings (30, 31; 30″, 31″); a plurality of second rolling bodies(51; 51″), which are interposed between said second and third rings (50,31; 50″, 31″) and adapted to roll on respective second tracks (52, 53;52″, 53″) of said second and third rings (50, 31; 50″, 31″); and alocking element (55; 55″) arranged in a standard configuration, whereinit allows the relative rotation of said third ring (31; 31″) and theother one (30; 50″) of said first ring and second ring (30, 50; 30″,50″); said locking element (55; 55″) being movable from said standardconfiguration to at least one first or second emergency configuration,wherein it prevents the relative rotation of said third ring (31; 31″)and said other one (30; 50″) of said first ring and second ring (30,50″; 30″, 50″) and allows the relative rotation of said third ring (31;31″) and said one (50; 30″) of said first ring and second ring (30, 50;30″, 50″); said first ring (30; 30″), said third ring (31, 31″) and saidsecond ring (50, 50″) being coaxial and extending about said axis (A);said second ring (31, 31″) being radially internal with respect to saidthird ring (31, 31″); said third ring (31, 31″) being radially internalwith said first ring (30, 30″); characterized in that said third ring(31, 31″) defines in a one piece one of said second tracks (52, 53; 52″,53″) and one of said first tracks (33, 34; 33″, 34″); said first tracks(33, 34; 33″, 34″) radially facing one another; said second tracks (52,53; 52″, 53″) radially facing one another; said first tracks (33, 34;33″, 34″) and said second tracks (52, 53; 52″, 53″) radially facing oneanother.
 29. The anti-torque rotor of claim 28, characterized in thatsaid second tracks (52, 53; 52″, 53″) are radially inner with respect tosaid first tracks (33, 34; 33″, 34″) relative to said axis (A). 30.(canceled)
 31. The anti-torque rotor of claim 28, characterized in thatsaid locking element (55; 55″) is slidable with respect to said thirdring (31; 31″) parallel to said first axis (A) between: an insertedposition, reached in said standard configuration and wherein saidlocking element (55; 55″) is at a first axial distance from said thirdring (31; 31″); and an extracted position, reached in said first orsecond emergency configuration, and wherein said locking element (55,55″) is at a second axial distance from said third ring (31, 31″),greater than said first axial distance.
 32. The anti-torque rotor ofclaim 28, characterized in that by comprising: two axially spaced ringsof first rolling bodies (51; 51″); and two axially spaced rings ofsecond rolling bodies (32; 32″).
 33. The anti-torque rotor of claim 32,characterized in that said second rolling bodies (51; 51″) and/or saidfirst rolling bodies (32; 32″) are axially pre-loaded.
 34. Theanti-torque rotor of claim 28, characterized in that said second rollingbodies (51; 51″) are conical roller.
 35. An anti-torque rotor (4) for ahelicopter (1), comprising: a mast (6), rotatable about a first axis(A); a plurality of blades (8), hinged on said mast (6), extending alongrespective second axes (B) transversal to said first axis (A) androtatable about respective said second axes (B) to vary the respectiveangles of attack; an element (16), sliding along said first axis (A)with respect to said mast (6), integrally rotating with said mast (6),and operatively connected to said blades (8) to cause the rotation ofsaid blades (8) about respective said second axes (B) following atranslation of said element (16) along said axis (A); a control rod(10), sliding axially along said first axis (A) with respect to saidmast (6) and angularly fixed with respect to said first axis (A); and afirst bearing (17) interposed between said control rod (10) and saidelement (16), sliding along said first axis (A) with respect to saidmast (6) and integrally with said control rod (10), and configured toenable the relative rotation of said element (16) with respect to saidcontrol rod (10) about said first axis (A) in a correct operatingcondition; said first bearing (17), in turn, comprising: a first ring(30) rotatable integrally with said element (16) about said first axis(A); a second ring (31) radially internal to said first ring (30) withrespect to said first axis (A) and sliding integrally with said controlrod (10) along said first axis (A); and a plurality of first rollingbodies (32), which are interposed between said first and second rings(30, 31) and adapted to roll on respective first tracks (33, 34) of saidfirst and second rings (30, 31); a third ring (50) sliding integrallywith said control rod (10) along said first axis (A) and angularly fixedwith respect to said first axis (A); a plurality of second rollingbodies (51), which are interposed between said second and third rings(31, 50) and adapted to roll on respective second tracks (52, 53) ofsaid second and third rings (31, 50); and a locking element (55)arranged in a standard configuration, wherein it prevents the relativerotation of said second and third rings (31, 50), when said firstbearing (17) is, in use, in a normal operating condition; said lockingelement (55) being movable from said standard configuration to at leasta first or second emergency configuration, wherein it makes said secondring (31) free to rotate with respect to said third ring (50) about saidfirst axis (A), when said first bearing (17) is, in use, in a failurecondition; said locking element (55), in turn, comprising: a main body(60); a fourth ring (65) fastened on said second ring (31) at least whensaid locking element (55) is arranged, in use, in said standardconfiguration; and at least one connection arm (70) interposed betweensaid main body (60) and said fourth ring (65), at least when saidlocking element (55) is arranged, in use, in said standardconfiguration; said locking element (55), when arranged, in use, in saidfirst or second emergency configuration, being slidable with respect tosaid third ring (50) parallel to said first axis (A) between: aninserted position, reached in said standard configuration and whereinsaid locking element (55) is at a first axial distance from said thirdring (50); and an extracted position, reached in said first or secondemergency configuration, and wherein said locking element (55) is at asecond axial distance from said third ring (50), greater than said firstaxial distance; characterized in that said rotor (4) comprises a cover(46) made of a transparent material and housing at least a part of saidmain body (60); said main body (60) comprising a band visible throughthe cover (46), when the locking element (55) is arranged in theextracted position.
 36. The rotor according to claim 35, characterizedin that said locking element (55) is angularly fixed with respect tosaid first axis (A) and is slidable, when arranged, in use, in saidstandard configuration, along said first axis (A) integrally with saidthird ring (50).
 37. The rotor according to claim 36, characterized inthat said fourth ring (65) is force-fitted by interference on saidsecond ring (31), when said locking element (55) is arranged, in use, insaid standard configuration.
 38. The rotor according to claim 37,characterized in that at least said fourth ring (65) is made of amaterial having a first thermal expansion coefficient greater than asecond thermal expansion coefficient of said second ring (31); saidfourth ring (65) being disengaged from said second ring (31), when saidlocking element (55) is in said first emergency configuration, reachedwhen the temperature of said first bearing (17) exceeds, in use, a firstthreshold value.
 39. The rotor according to claim 35, characterized inthat said main body (55) and said fourth ring (65) are separated, whensaid locking element (55) is in a second emergency configuration,reached at least when the torque acting, in use, on said second ring(31) exceeds a second threshold value.
 40. The rotor according to claim39, characterized in that said arm (70) is breakable when said torqueacting, in use, on said second ring (31) and on said fourth ring (65) isgreater than said second threshold value, so as to arrange said lockingelement (55) in said second emergency configuration.
 41. The rotoraccording to claim 40, characterized in that it comprises elastic means(100) interposed, at least indirectly, between said third ring (50) andsaid locking element (55); said elastic means (100) elasticallypreloading said locking element (55) towards said extracted position.42. The rotor according to claim 35, characterized in that it comprises:at least one pin (81) connected, at least indirectly, to said third ring(50) and extending radially to said first axis (A); and at least oneaxial slot (76) carried by said locking element (55), having said pin(81) pass radially through it and axially slidable with respect the saidpin (81), at least when said locking element (55) is in said first orsecond emergency configuration.
 43. The rotor according to claim 42,characterized in that said locking element (55) further comprises: aplurality of said slots (76) angularly spaced apart from each otheraround said first axis (A) and through which respective said pins (81)pass; and a plurality of said arms (70) angularly spaced apart from eachother around said first axis (A); said slots (76) and said arms (70)variating with one another around said first axis (A).
 44. The rotoraccording to claim 38, characterized in that said rotor (4) comprises afifth ring (85) arranged in axial abutment against said pins (81) and towhich said elastic means (100) are connected.
 45. The rotor according toclaim 35, characterized in that said second ring (31) comprises ashoulder (37) axially interposed between said first rolling bodies (32)and extending over larger radial distances from said first axis (A) withrespect to said second tracks (33, 34).
 46. An anti-torque rotor (4) fora helicopter (1), comprising: a mast (6), rotatable about a first axis(A); a plurality of blades (8), hinged on said mast (6), extending alongrespective second axes (B) transversal to said first axis (A) androtatable about respective said second axes (B) to vary the respectiveangles of attack; an element (16), sliding along said first axis (A)with respect to said mast (6), integrally rotating with said mast (6),and operatively connected to said blades (8) to cause the rotation ofsaid blades (8) about respective said second axes (B) following atranslation of said element (16) along said axis (A); a control rod(10), sliding axially along said first axis (A) with respect to saidmast (6) and angularly fixed with respect to said first axis (A); and afirst bearing (17) interposed between said control rod (10) and saidelement (16), sliding along said first axis (A) with respect to saidmast (6) and integrally with said control rod (10), and configured toenable the relative rotation of said element (16) with respect to saidcontrol rod (10) about said first axis (A) in a correct operatingcondition; said first bearing (17), in turn, comprising: a first ring(30) rotatable integrally with said element (16) about said first axis(A); a second ring (31) radially internal to said first ring (30) withrespect to said first axis (A) and sliding integrally with said controlrod (10) along said first axis (A); and a plurality of first rollingbodies (32), which are interposed between said first and second rings(30, 31) and adapted to roll on respective first tracks (33, 34) of saidfirst and second rings (30, 31); a third ring (50) sliding integrallywith said control rod (10) along said first axis (A) and angularly fixedwith respect to said first axis (A); a plurality of second rollingbodies (51), which are interposed between said second and third rings(31, 50) and adapted to roll on respective second tracks (52, 53) ofsaid second and third rings (31, 50); and a locking element (55)arranged in a standard configuration, wherein it prevents the relativerotation of said second and third rings (31, 50), when said firstbearing (17) is, in use, in a normal operating condition; said lockingelement (55) being movable from said standard configuration to at leasta first or second emergency configuration, wherein it makes said secondring (31) free to rotate with respect to said third ring (50) about saidfirst axis (A), when said first bearing (17) is, in use, in a failurecondition; said locking element (55), in turn, comprising: a main body(60); a fourth ring (65) fastened on said second ring (31) at least whensaid locking element (55) is arranged, in use, in said standardconfiguration; and at least one connection arm (70) interposed betweensaid main body (60) and said fourth ring (65), at least when saidlocking element (55) is arranged, in use, in said standardconfiguration; said fourth ring (65) being force-fitted by interferenceon said second ring (31), when said locking element (55) is arranged, inuse, in said standard configuration; characterized in that at least saidfourth ring (65) is made of a material having a first thermal expansioncoefficient greater than a second thermal expansion coefficient of saidsecond ring (31); said fourth ring (65) being disengaged from saidsecond ring (31), when said locking element (55) is in said firstemergency configuration, reached when the temperature of said firstbearing (17) exceeds, in use, a first threshold value.
 47. The rotoraccording to claim 46, characterized in that said locking element (55)is angularly fixed with respect to said first axis (A) and is slidable,when arranged, in use, in said standard configuration, along said firstaxis (A) integrally with said third ring (50).
 48. The rotor accordingto claim 46, characterized in that said main body (55) and said fourthring (65) are separated, when said locking element (55) is in a secondemergency configuration, reached at least when the torque acting, inuse, on said second ring (31) exceeds a second threshold value.
 49. Therotor according to claim 48, characterized in that said arm (70) isbreakable when said torque acting, in use, on said second ring (31) andon said fourth ring (65) is greater than said second threshold value, soas to arrange said locking element (55) in said second emergencyconfiguration.
 50. The rotor according to claim 46, characterized inthat said locking element (55), when arranged, in use, in said first orsecond emergency configuration, is slidable with respect to said thirdring (50) parallel to said first axis (A) between: an inserted position,reached in said standard configuration and wherein said locking element(55) is at a first axial distance from said third ring (50); and anextracted position, reached in said first or second emergencyconfiguration, and wherein said locking element (55) is at a secondaxial distance from said third ring (50), greater than said first axialdistance.
 51. The rotor according to claim 50, characterized in that itcomprises elastic means (100) interposed, at least indirectly, betweensaid third ring (50) and said locking element (55); said elastic means(100) elastically preloading said locking element (55) towards saidextracted position.
 52. The rotor according to claim 44, characterizedin that said rotor (4) comprises a cover (46) made of a transparentmaterial and housing at least a part of said main body (60); said mainbody (60) comprising a band visible through the cover (46), when thelocking element (55) is arranged in the extracted position.
 53. Therotor according to claim 46, characterized in that it comprises: atleast one pin (81) connected, at least indirectly, to said third ring(50) and extending radially to said first axis (A); and at least oneaxial slot (76) carried by said locking element (55), having said pin(81) pass radially through it and axially slidable with respect the saidpin (81), at least when said locking element (55) is in said first orsecond emergency configuration.
 54. The rotor according to claim 53,characterized in that said locking element (55) further comprises: aplurality of said slots (76) angularly spaced apart from each otheraround said first axis (A) and through which respective said pins (81)pass; and a plurality of said arms (70) angularly spaced apart from eachother around said first axis (A); said slots (76) and said arms (70)variating with one another around said first axis (A).
 55. The rotoraccording to claim 51, characterized in that said rotor (4) comprises afifth ring (85) arranged in axial abutment against said pins (81) and towhich said elastic means (100) are connected.
 56. The rotor according toclaim 46, characterized in that said second ring (31) comprises ashoulder (37) axially interposed between said first rolling bodies (32)and extending over larger radial distances from said first axis (A) withrespect to said second tracks (33, 34).
 57. An anti-torque rotor (4) fora helicopter (1), comprising: a mast (6), rotatable about a first axis(A); a plurality of blades (8), hinged on said mast (6), extending alongrespective second axes (B) transversal to said first axis (A) androtatable about respective said second axes (B) to vary the respectiveangles of attack; an element (16), sliding along said first axis (A)with respect to said mast (6), integrally rotating with said mast (6),and operatively connected to said blades (8) to cause the rotation ofsaid blades (8) about respective said second axes (B) following atranslation of said element (16) along said axis (A); a control rod(10), sliding axially along said first axis (A) with respect to saidmast (6) and angularly fixed with respect to said first axis (A); and afirst bearing (17) interposed between said control rod (10) and saidelement (16), sliding along said first axis (A) with respect to saidmast (6) and integrally with said control rod (10), and configured toenable the relative rotation of said element (16) with respect to saidcontrol rod (10) about said first axis (A) in a correct operatingcondition; said first bearing (17), in turn, comprising: a first ring(30) rotatable integrally with said element (16) about said first axis(A); a second ring (31) radially internal to said first ring (30) withrespect to said first axis (A) and sliding integrally with said controlrod (10) along said first axis (A); and a plurality of first rollingbodies (32), which are interposed between said first and second rings(30, 31) and adapted to roll on respective first tracks (33, 34) of saidfirst and second rings (30, 31); a third ring (50) sliding integrallywith said control rod (10) along said first axis (A) and angularly fixedwith respect to said first axis (A); a plurality of second rollingbodies (51), which are interposed between said second and third rings(31, 50) and adapted to roll on respective second tracks (52, 53) ofsaid second and third rings (31, 50); and a locking element (55)arranged in a standard configuration, wherein it prevents the relativerotation of said second and third rings (31, 50), when said firstbearing (17) is, in use, in a normal operating condition; said lockingelement (55) being movable from said standard configuration to at leasta first or second emergency configuration, wherein it makes said secondring (31) free to rotate with respect to said third ring (50) about saidfirst axis (A), when said first bearing (17) is, in use, in a failurecondition; said locking element (55), when arranged, in use, in saidfirst or second emergency configuration, being slidable with respect tosaid third ring (50) parallel to said first axis (A) between: aninserted position, reached in said standard configuration and whereinsaid locking element (55) is at a first axial distance from said thirdring (50); and an extracted position, reached in said first or secondemergency configuration, and wherein said locking element (55) is at asecond axial distance from said third ring (50), greater than said firstaxial distance; characterized in that it comprises elastic means (100)interposed, at least indirectly, between said third ring (50) and saidlocking element (55); said elastic means (100) elastically preloadingsaid locking element (55) towards said extracted position.
 58. The rotoraccording to claim 57, characterized in that said locking element (55)is angularly fixed with respect to said first axis (A) and is slidable,when arranged, in use, in said standard configuration, along said firstaxis (A) integrally with said third ring (50).
 59. The rotor accordingto claim 57, characterized in that said locking element (55), in turn,comprises: a main body (60); a fourth ring (65) fastened on said thirdring (50) at least when said locking element (55) is arranged, in use,in said standard configuration; and at least one connection arm (70)interposed between said main body (60) and said fourth ring (65), atleast when said locking element (55) is arranged, in use, in saidstandard configuration.
 60. The rotor according to claim 59,characterized in that said fourth ring (65) is force-fitted byinterference on said second ring (31), when said locking element (55) isarranged, in use, in said standard configuration.
 61. The rotoraccording to claim 60, characterized in that at least said fourth ring(65) is made of a material having a first thermal expansion coefficientgreater than a second thermal expansion coefficient of said second ring(31); said fourth ring (65) being disengaged from said second ring (31),when said locking element (55) is in said first emergency configuration,reached when the temperature of said first bearing (17) exceeds, in use,a first threshold value.
 62. The rotor according to claim 59,characterized in that said main body (55) and said fourth ring (65) areseparated, when said locking element (55) is in a second emergencyconfiguration, reached at least when the torque acting, in use, on saidsecond ring (31) exceeds a second threshold value.
 63. The rotoraccording to claim 62, characterized in that said arm (70) is breakablewhen said torque acting, in use, on said second ring (31) and on saidfourth ring (65) is greater than said second threshold value, so as toarrange said locking element (55) in said second emergencyconfiguration.
 64. The rotor according to claim 62, characterized inthat said rotor (4) comprises a cover (46) made of a transparentmaterial and housing at least a part of said main body (60); said mainbody (60) comprising a band visible through the cover (46), when thelocking element (55) is arranged in the extracted position.
 65. Therotor according to claim 57, characterized in that it comprises: atleast one pin (81) connected, at least indirectly, to said third ring(50) and extending radially to said first axis (A); and at least oneaxial slot (76) carried by said locking element (55), having said pin(81) pass radially through it and axially slidable with respect the saidpin (81), at least when said locking element (55) is in said first orsecond emergency configuration.
 66. The rotor according to claim 65,characterized in that said locking element (55) further comprises: aplurality of said slots (76) angularly spaced apart from each otheraround said first axis (A) and through which respective said pins (81)pass; and a plurality of said arms (70) angularly spaced apart from eachother around said first axis (A); said slots (76) and said arms (70)variating with one another around said first axis (A).
 67. The rotoraccording to claim 66, characterized in that said rotor (4) comprises afifth ring (85) arranged in axial abutment against said pins (81) and towhich said elastic means (100) are connected.
 68. The rotor according toclaim 55, characterized in that said second ring (31) comprises ashoulder (37) axially interposed between said first rolling bodies (32)and extending over larger radial distances from said first axis (A) withrespect to said second tracks (33, 34).
 69. An anti-torque rotor (4) fora helicopter (1), comprising: a mast (6), rotatable about a first axis(A); a plurality of blades (8), hinged on said mast (6), extending alongrespective second axes (B) transversal to said first axis (A) androtatable about respective said second axes (B) to vary the respectiveangles of attack; an element (16), sliding along said first axis (A)with respect to said mast (6), integrally rotating with said mast (6),and operatively connected to said blades (8) to cause the rotation ofsaid blades (8) about respective said second axes (B) following atranslation of said element (16) along said axis (A); a control rod(10), sliding axially along said first axis (A) with respect to saidmast (6) and angularly fixed with respect to said first axis (A); and afirst bearing (17) interposed between said control rod (10) and saidelement (16), sliding along said first axis (A) with respect to saidmast (6) and integrally with said control rod (10), and configured toenable the relative rotation of said element (16) with respect to saidcontrol rod (10) about said first axis (A) in a correct operatingcondition; said first bearing (17), in turn, comprising: a first ring(30) rotatable integrally with said element (16) about said first axis(A); a second ring (31) radially internal to said first ring (30) withrespect to said first axis (A) and sliding integrally with said controlrod (10) along said first axis (A); and a plurality of first rollingbodies (32), which are interposed between said first and second rings(30, 31) and adapted to roll on respective first tracks (33, 34) of saidfirst and second rings (30, 31); a third ring (50) sliding integrallywith said control rod (10) along said first axis (A) and angularly fixedwith respect to said first axis (A); a plurality of second rollingbodies (51), which are interposed between said second and third rings(31, 50) and adapted to roll on respective second tracks (52, 53) ofsaid second and third rings (31, 50); and a locking element (55)arranged in a standard configuration, wherein it prevents the relativerotation of said second and third rings (31, 50), when said firstbearing (17) is, in use, in a normal operating condition; said lockingelement (55) being movable from said standard configuration to at leasta first or second emergency configuration, wherein it makes said secondring (31) free to rotate with respect to said third ring (50) about saidfirst axis (A), when said first bearing (17) is, in use, in a failurecondition; characterized in that it comprises: at least one pin (81)angularly fixed and connected, at least indirectly, to said third ring(50) and extending radially to said first axis (A); and at least oneaxial slot (76) integrally carried by said locking element (55), havingsaid pin (81) pass radially through it and axially slidable with respectthe said pin (81), at least when said locking element (55) is in saidfirst or second emergency configuration.
 70. The rotor according toclaim 69, characterized in that said locking element (55) is angularlyfixed with respect to said first axis (A) and is slidable, whenarranged, in use, in said standard configuration, along said first axis(A) integrally with said third ring (50).
 71. The rotor according toclaim 69, characterized in that said locking element (55), in turn,comprises: a main body (60); a fourth ring (65) fastened on said secondring (31) at least when said locking element (55) is arranged, in use,in said standard configuration; and at least one connection arm (70)interposed between said main body (60) and said fourth ring (65), atleast when said locking element (55) is arranged, in use, in saidstandard configuration.
 72. The rotor according to claim 71,characterized in that said fourth ring (65) is force-fitted byinterference on said second ring (31), when said locking element (55) isarranged, in use, in said standard configuration.
 73. The rotoraccording to claim 72, characterized in that at least said fourth ring(65) is made of a material having a first thermal expansion coefficientgreater than a second thermal expansion coefficient of said second ring(31); said fourth ring (65) being disengaged from said second ring (31),when said locking element (55) is in said first emergency configuration,reached when the temperature of said first bearing (17) exceeds, in use,a first threshold value.
 74. The rotor according to claim 71,characterized in that said main body (55) and said fourth ring (65) areseparated, when said locking element (55) is in a second emergencyconfiguration, reached at least when the torque acting, in use, on saidsecond ring (31) exceeds a second threshold value.
 75. The rotoraccording to claim 74, characterized in that said arm (70) is breakablewhen said torque acting, in use, on said second ring (31) and on saidfourth ring (65) is greater than said second threshold value, so as toarrange said locking element (55) in said second emergencyconfiguration.
 76. The rotor according to claim 69, characterized inthat said locking element (55), when arranged, in use, in said first orsecond emergency configuration, is slidable with respect to said thirdring (50) parallel to said first axis (A) between: an inserted position,reached in said standard configuration and wherein said locking element(55) is at a first axial distance from said third ring (50); and anextracted position, reached in said first or second emergencyconfiguration, and wherein said locking element (55) is at a secondaxial distance from said third ring (50), greater than said first axialdistance.
 77. The rotor according to claim 76, characterized in that itcomprises elastic means (100) interposed, at least indirectly, betweensaid third ring (50) and said locking element (55); said elastic means(100) elastically preloading said locking element (55) towards saidextracted position.
 78. The rotor according to claim 71, characterizedin that said rotor (4) comprises a cover (46) made of a transparentmaterial and housing at least a part of said main body (60); said mainbody (60) comprising a band visible through the cover (46), when thelocking element (55) is arranged in the extracted position.
 79. Therotor according to 69, characterized in that said locking element (55)further comprises: a plurality of said slots (76) angularly spaced apartfrom each other around said first axis (A) and through which respectivesaid pins (81) pass; and a plurality of said arms (70) angularly spacedapart from each other around said first axis (A); said slots (76) andsaid arms (70) variating with one another around said first axis (A).80. The rotor according to claim 77, characterized in that said rotor(4) comprises a fifth ring (85) arranged in axial abutment against saidpins (81) and to which said elastic means (100) are connected.
 81. Therotor according to claim 69, characterized in that said second ring (31)comprises a shoulder (37) axially interposed between said first rollingbodies (32) and extending over larger radial distances from said firstaxis (A) with respect to said second tracks (33, 34).
 82. A helicoptercomprising: a fuselage (2); a main rotor (3); and an anti-torque rotor(4) according to claim 1.